S.R. Johns

The influence of allylic oxygen on the CD of skew dienes

Abstract The CD of eight compounds each containing a conjugated diene system is discussed. In five of these the sign of the Cotton effect attributable to the lowest energy diene absorption band is at variance with the sign predicted by the rules relating sign to diene helicity. Each of the five compounds incorporates one or more oxygen substituents (hydroxyl, methoxyl, (1-carboxyvinyl)oxy) allylic to the diene system. If its is assumed that the helicity of the system Oue5f8Cue5f8Cue5fbCue5f8 may have a larger influence on the CD than the helicity of the diene system itself, these results are consistently explained.

STRUCTURE OF IPOMINE, A NEW ALKALOID FROM IPOMOEA MURICATA JACQ

Abstract Studies on the basic fraction from Ipomoea muricata Jacq. seeds, grown in Senegal, resulted in the isolation of two hexahydroindolizine alkaloids, the previously described ipalbidine and a new alkaloid, ipomine, C 30 H 35 NO 8 , the structure of which is established as 1-β-ipalbidinyl-4-p-coumaroyl- d -glucopyranoside.

The absolute molecular structure of podopetaline

Abstract X-ray analysis of crystals of podopetaline hydrobromide, C 20 H 33 N 3 ·HBr, has established the absolute structure of podopetaline, an alkaloid from Podopetalum ormondii F. Muell. The crystals are orthorhombic, with unit cell dimensions, a = 6·619, b = 10·907, c = 26·806 A, Z = 4, the space group being P2 1 2 1 2 1 . The intensity data were measured with CuKα radiation on a single-crystal diffractometer. The crystal structure was solved by the heavy atom method and refined by difference and least-squares procedures to a final R index of 0·069 for the 849 observed terms. The absolute chirality has been defined by Bijvoets technique. Podopetaline (I) therefore provides an absolute chirality reference for Ormosia alkaloids which was not previously available.